I'm late, but I wanted to get my pals takes on this, too. For me, the biggest thing might be being 6v6. A single extra player on each team can go a long way towards making more interesting team compositions.

Both the pals I've been playing with brought up the "team-up" mechanic. We've been having a good time playing around with these duos/trios, and there's definitely a lot of interesting things they can do with it in the future, even if it kinda seems like a balancing headache.

Then, of course, it's also got the value of being a Marvel IP. That's not specifically better or worse than Overwatch, but it's definitely already helped the game attract so many players.

I wouldn't have the confidence to call it "the Overwatch killer" or anything, but it'll certainly be a real competitor as Overwatch bleeds itself out.